JP3189911B2 - Sand composition for molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sand composition for molding using reclaimed sand, and more particularly to a mold composition which is less likely to release harmful decomposition products during the production of castings and is less likely to cause gas defects in the resulting castings. The present invention relates to an obtainable sand composition for molding.

[0002]

2. Description of the Related Art Conventionally, the following method has been adopted for the production of a mold from the viewpoint of effective utilization of sand. That is, sand is collected from a used mold, and a binder or the like attached to the surface of the sand is removed to obtain recycled sand. Then, a small amount of fresh sand is added to the reclaimed sand, and a binder and a catalyst for curing the binder are added to prepare a mold.
At this time, the reclaimed sand used must have a small amount of a binder or the like attached to its surface. Because, if a mold is obtained using a large amount of binder or the like, the binder or the like adhering to the recycled sand at the time of casting production releases harmful decomposition products, and the working environment is deteriorated. This is because there are times. Also, components such as a binder adhering to the reclaimed sand are dissolved in the molten metal at the time of pouring, and the dissolved components become bubbles when the molten metal is cooled, so that a gas defect or the like occurs in the obtained casting. is there.

For this reason, LOI management has been conventionally performed to control the amount of a binder or the like adhering to the surface of reclaimed sand. LOI management is based on organic substances adhering to sand (mainly binders and catalysts for curing binders)
And is performed in the following manner. That is, this is a management method in which the sampled regenerated sand is baked at 1000 ° C. for about 2 hours and the weight loss rate at that time is measured. Therefore, the smaller the weight loss rate, the less the organic substance adheres to the sand, and the weight loss rate is controlled so as to be always less than a certain weight.

[0004] By the way, furan resins have been conventionally used as binders when preparing molds (Japanese Patent Publication No. 39-1543, etc.), and phosphorus compounds (JP-A-47-16324) have been used as curing catalysts for furan resins. And sulfonic acid compounds (JP-A-53-30421 and JP-A-59-113952). When a mold is produced using a furan resin as a binder and a sulfonic acid-based compound such as benzenesulfonic acid or toluenesulfonic acid as a curing catalyst, if the LOI management described above is performed, the management of recycled sand is relatively difficult. It was good. That is, the disadvantage of using a sulfonic acid-based compound as a curing catalyst, which is mainly the release of decomposition products during the production of castings, was successfully prevented, which was preferable. However, when a mold is produced using a furan resin as a binder and a phosphorus compound as a curing catalyst, even if the LOI is managed as described above, the management of the recycled sand is not sufficient. That is, it was not possible to effectively prevent the disadvantage of using a phosphorus compound as a curing catalyst, mainly that gas defects occur in a casting.

[0005]

SUMMARY OF THE INVENTION
The present inventors, when using a phosphorus compound-based curing catalyst,
It was investigated why gas defects occur in the obtained casting even if the mold is manufactured by performing LOI management. As a result, L
It was concluded that OI management only controls the amount of organic matter in the reclaimed sand and does not control the type of organic matter. That is, it was concluded that gas defects occurred on the casting surface because a large amount of phosphorus or nitrogen was contained in the mold. Therefore, the present invention performs LOI management of the reclaimed sand and controls the amount of phosphorus or nitrogen contained in the reclaimed sand while producing a mold, so that a gas defect or the like is hardly generated in the obtained casting. It is like that.

[0006]

That is, the present invention provides a method for producing a reclaimed sand used for repeatedly producing a mold, a binder comprising an acid-curable furan resin, phosphoric acid, condensed phosphoric acid, a phosphoric acid ester and a phosphoric acid. One or more phosphorus compound-based curing catalysts selected from the group consisting of acid salts, wherein the difference between the loss on burning of the regenerated sand and the loss on burning of the fresh sand is 4.0% by weight or less; The phosphorus content in the reclaimed sand is 0.008-0.
The present invention relates to a sand composition for molding, which is 55% by weight.

The reclaimed sand used in the present invention is obtained by reclaiming the sand in a mold once used by a mechanical abrasion method or a roasting method. Generally, those regenerated by abrasion method are preferable because of high yield and economical excellence. Silica sand, chromite sand, zircon sand, olivine sand, alumina sand, etc., having quartz as a main component, are used as the sand body of the reclaimed sand. In fact, when making a mold using recycled sand, it is rare to use 100% by weight of recycled sand, and a small amount of fresh sand is added.

An acid-curable furan resin is used as a binder in order to bond regenerated sand and fresh sand to obtain a sufficient strength of the resulting mold. As the furan resin, various conventionally known ones can be used. For example, furfuryl alcohol, furfuryl alcohol-urea resin, furfuryl alcohol-formaldehyde resin, furfuryl alcohol-phenol resin, furfuryl alcohol-resorcinol resin, furfuryl Alcohol-melamine resins, furfuryl alcohol polymers and the like are used alone or in combination. Various modifiers may be added to these furan resins in combination. In order to further improve the strength of the mold, a silane coupling agent may be added to the furan resin. As the silane coupling agent, for example, γ- (2-
Amino) aminopropylmethyldimethoxysilane, γ-
Aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane and the like are used.

Phosphorus compounds which are curing catalysts for accelerating the curing of furan resins include phosphoric acid, condensed phosphoric acid,
Phosphate esters and phosphates are used alone or as a mixture. As the phosphoric acid ester, methyl phosphoric acid or ethyl phosphoric acid is typical, but other phosphoric acid esters can also be used. As the phosphate, potassium phosphate or potassium hydrogen phosphate is typical, but other phosphates can also be used. Although only these phosphorus compounds may be used as the curing catalyst, other curing catalysts may be used in combination with the phosphorus compound. Other types of curing catalysts include alkyl or aryl sulfonic acids such as methyl sulfonic acid, ethyl sulfonic acid, benzene sulfonic acid, toluene sulfonic acid, xylene sulfonic acid, organic acids such as carboxylic acids, and inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid. Acids and the like are used. The amount of the other type of curing catalyst used is appropriately adjusted according to the desired curing time.

What is important in the present invention is to adjust the above-mentioned ratio of loss on ignition of the regenerated sand as follows. That is, the difference between the burning loss ratio of the regenerated sand and the burning loss ratio of the fresh sand is adjusted to 4.0% by weight or less. Here, in addition to adjusting only the burning loss ratio of the reclaimed sand,
The reason for adjusting the difference from the burning loss ratio of the new sand is to accurately measure the amount of the organic substance adhering to the reclaimed sand.
That is, if only the burning weight loss ratio of the regenerated sand is adjusted, the organic substance inherently contained in the sand is included in the weight loss ratio. When the difference between the burning loss ratio of the regenerated sand and the burning loss ratio of the new sand exceeds 4.0% by weight, the generation of gas from the mold increases, and gas defects such as pinholes easily occur in the obtained casting, which is not preferable. .

The burning loss ratio of the regenerated sand and the burning loss ratio of the fresh sand are measured as follows. First, the weight (k) of the crucible used for measuring the ignition loss ratio is accurately measured. On the other hand, after the sand to be tested (regenerated sand or fresh sand) is dried at 105 ° C. for 1 hour, about 10.0 gr of the sand to be tested is collected, and the weight (w ₀ ) of the sand to be tested is accurately weighed. After putting this test sand in a crucible and exploding it in a muffle furnace at 1000 ° C for 2 hours,
The crucible is taken out, cooled to room temperature, and then stored in a desiccator for drying. Then, the weight (k + w ₁ ) is accurately weighed while the test sand is placed in the crucible. By subtracting the weight (k) of the crucible from this weight, the weight (w ₁ ) of the sand to be tested after burning can be measured. Then, [(w ₁ −w ₀ )
/ W ₁ ] × 100 to determine the burning loss ratio (% by weight). This burning loss ratio is determined for recycled sand and fresh sand, and the difference is made to be 4.0% by weight or less.

Further, in the present invention, the difference in the ignition loss ratio between the recycled sand and the fresh sand is set to 4.0% by weight or less,
It is necessary to make the phosphorus content in the reclaimed sand 0.008 to 0.55% by weight. If the phosphorus content in the reclaimed sand exceeds 0.55% by weight, a reaction takes place at the interface between the resulting mold and the molten metal to generate iron phosphide, which causes a pock-like defect on the casting surface, which is not preferable. Conversely, in order to reduce the phosphorus content to less than 0.008% by weight, regeneration must be repeated many times or a powerful regeneration method must be used, which is not economical. In addition, the measuring method of the phosphorus content in a reproduction | regeneration sand is as follows. That is, the reclaimed sand is finely pulverized to 150 mesh or less and used as a sample.
It is a method of measuring at. Also preferably, nitrogen
By further increasing the elemental content to 0.004-0.22% by weight
is there. If the nitrogen content exceeds 0.22% by weight, the ammonium compound (NH _x ) in the reclaimed sand dissolves in the molten metal during the process of filling the molten metal in the mold, and when the molten metal solidifies, it is converted into nitrogen gas as an external gas. And the locus thereof tends to cause pinholes in the casting. Conversely, in order to reduce the nitrogen content to less than 0.004% by weight, regeneration must be repeated many times or a powerful regeneration method must be used, which is not economical. The method for measuring the nitrogen content in the reclaimed sand is as follows. That is, the recycled sand is 15
This is a method in which a sample finely pulverized to 0 mesh or less is used as a sample and measured by Kjeldahl nitrogen analysis. Therefore,
In the present invention, the difference in the ignition loss ratio between the regenerated sand and the new sand is set to 4.0% by weight or less, and the phosphorus content in the regenerated sand is adjusted.
Should be 0.008 to 0.55% by weight.
However, in particular , the phosphorus content in the reclaimed sand is 0.008 to 0.55% by weight, and the nitrogen content in the reclaimed sand is 0.004 to 0.5%.
Preferably it is 22% by weight. With such adjustment, pock-shaped defects, pinholes, and the like are less likely to occur in the obtained casting.

As described above, in order to reduce the amount of organic substances adhering to the reclaimed sand and to reduce the phosphorus and nitrogen contents, a furan resin as a binder having a low phosphorus or nitrogen content is used. Or a phosphorus compound having a low content of phosphorus or nitrogen as a curing catalyst is preferably used. It is also preferable to repeat the reproduction several times. In order to repeat the playback several times, it is necessary to perform two or more passes when using a single player, and to connect them in series when using several players. General.

[0014]

EXAMPLE 1 A nitrogen content of 1.0% by weight based on 100 parts by weight of recycled sand.
0.8 parts by weight of furan resin and 0.36 parts by weight of 85% by weight phosphoric acid were added and kneaded to obtain a sand composition for molding. In addition, this reclaimed sand was reclaimed using fresh sand or reclaimed sand, sand collected from a mold prepared using a furan resin and a phosphorus compound-based curing catalyst, using a crusher, and an M-type rotary reclaimer manufactured by Nippon Casting Co., Ltd. And the burning loss ratio (LO
I) The desired number of passes through the rotary crema to achieve a nitrogen content and a phosphorus content. Using this sand composition for molding, a Daido donut-type test mold was prepared. The shape of this donut type test mold is shown in FIGS.
40mm on a hollow circular donut
A gate 1 of φ and a riser 2 of 90 mmφ are attached.

Then, the molten metal was poured into a donut-shaped test mold to obtain a casting. Using the obtained casting, the number of gas defects on the casting surface (per casting) by liquid penetration testing
Was measured, and the results are shown in Table 1. The outline of the liquid penetrant inspection method is as follows. 1) Pretreatment: Clean the casting surface. 2) Penetration treatment: Apply a penetrating liquid to the casting surface by spraying method and wet it sufficiently. 3) Cleaning treatment: After 20 minutes have passed since the permeation treatment, the excess permeation liquid adhering to the surface other than the gas defect surface is removed by the cleaning liquid. 4) Developing process: A developing solution is applied to the casting surface after the cleaning process, and the penetrant remaining in the gas defect is sucked out to the casting surface. 5) Observation: The support pattern formed by the development processing is visually observed, and the number of gas defects is measured.

[0016]

[Table 1] In Table 1, the item indicated as LOI is obtained by subtracting the burning loss ratio of fresh sand from the burning loss ratio of recycled sand.

Examples 2 to 10 The difference in the loss on ignition ratio (LOI) between recycled sand and fresh sand, the phosphorus content in recycled sand and the nitrogen content in recycled sand were changed as described in Table 1. A sand composition for molding was obtained in the same manner as in Example 1, a casting was obtained in the same manner as in Example 1, and the number of gas defects was measured. The results are shown in Table 1.

Comparative Example 1 Nitrogen content was 6.0% by weight based on 100 parts by weight of recycled sand.
0.8 parts by weight of furan resin and 0.36 parts by weight of 85% by weight phosphoric acid were added and kneaded to obtain a sand composition for molding. The method for regenerating the recycled sand is described in Example 1.
The same method as that described above was applied, and the loss on ignition ratio (LOI) and nitrogen
The content and the phosphorus content were as shown in Table 1 . Using this sand composition for molding, a casting was obtained in the same manner as in Example 1, and the number of gas defects on the surface of the casting was measured in the same manner as in Example 1. The results are shown in Table 1.

Comparative Examples 2 to 10 The difference in the loss on ignition ratio (LOI) between the reclaimed sand and the fresh sand, the phosphorus content in the reclaimed sand and the nitrogen content in the reclaimed sand were changed as described in Table 1. A sand composition for molding was obtained in the same manner as in Comparative Example 1, a casting was obtained in the same manner as in Comparative Example 1, and the number of gas defects was measured. The results are shown in Table 1.

Examples 11 to 13 and Comparative Example 11 After a casting was obtained using the mold obtained in Example 1, the mold was broken to collect sand, and the sand was regenerated to obtain recycled sand. Was. With respect to the recycled sand, the difference in the ignition loss ratio between the recycled sand and the fresh sand (LOI), the phosphorus content in the recycled sand, and the nitrogen content in the recycled sand were adjusted as shown in Table 2. The sand was regenerated by the same method as described in Example 1, and the number of times of reproduction is shown in Table 2. Using the recycled sand, a sand composition for molding was obtained in the same manner as in Example 1, and a casting was obtained in the same manner as in Example 1. The number of gas defects on the casting surface was as shown in Table 2.

[0021]

As described above, the sand composition for molding according to the present invention has a specific burning loss ratio as reclaimed sand, a specific phosphorus content , and a
Ri is is obtained by employing the one with a nitrogen content in the specified amounts. Therefore, the mold obtained using this molding sand composition has a very low content of organic substances in the mold,
In addition, the content of phosphorus and, in some cases, nitrogen is small, and if a casting is produced with this mold, phosphorus can be prevented from reacting at the interface between the molten metal and the mold to form iron phosphide and the like, and
In some cases, dissolution of the nitrogen compound in the molten metal can be prevented. Therefore, it is possible to prevent pock-like defects due to iron phosphide, etc. on the obtained casting surface, and also to prevent generation of defects such as pinholes due to release of nitrogen gas in the molten metal upon cooling. Thus, there is an effect that a casting having a beautiful surface can be obtained. In addition, since the molding composition sand composition according to the present invention uses a phosphorus compound instead of a sulfonic acid compound as a curing catalyst for a furan resin, a mold obtained using the molding composition sand composition is used. Even when the molten metal is poured, harmful substances due to the decomposition of the sulfonic acid-based curing catalyst are less likely to be released, and the working environment at the time of casting production can be prevented from deteriorating.

[Brief description of the drawings]

FIG. 1 is a plan view of a donut type test mold used in an example.

FIG. 2 is a side view of the donut type test mold shown in FIG.

[Table 2]

Continuation of the front page (56) References JP-A-59-45057 (JP, A) JP-A-57-22842 (JP, A) JP-A-60-37240 (JP, A) JP-A-58-53344 (JP) , A) JP-A-57-58948 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22C 1/00-1/26

Claims (2)

(57) [Claims] 1. One kind selected from the group consisting of recycled sand used for repeatedly producing a mold, a binder made of an acid-curable furan resin, and phosphoric acid, condensed phosphoric acid, a phosphoric acid ester and a phosphate. Or two or more phosphorus compound-based curing catalysts, wherein the difference between the weight loss ratio of the regenerated sand and the weight loss of the fresh sand is 4.0% by weight or less, and the phosphorus content in the regenerated sand is 0% or less. 0.0008 to 0.55% by weight. 2. The recycled sand has a nitrogen content of 0.004 to 0.5.
The sand composition for molding according to claim 1, which is 22% by weight.